In recent years, the population has become increasingly aware of atmospheric pollution by pollutants, for example sulfur dioxide, nitrogen oxides, carcinogenic organic compounds, etc., and the damage increasingly caused by these substances, not only in nature but also on buildings, monuments and the like. In attempting to preserve as well as possible works of art and other objects of cultural or art-historical interest for future generations in spite of the adverse environmental conditions, a very wide variety of preservation measures have been taken and, of course, particular attempts have been made to screen valuable objects against corrosive environmental conditions. Thus, external protective glazing, for example, is the method which is customary today for protection of historical, corrosion-endangered glass paintings, in particular in medieval church windows.
However, it is not easy to determine the extent to which screening of this type actually fulfills the expectations which are made of them. The most reliable method would undoubtedly be direct examination of the object to be protected for corrosion effects. However, this can in most cases only be carried out with difficulty or not at all since examinations of this type must generally not be carried out on site but instead in the laboratory, which causes transport problems; in addition, these examinations are usually not possible without damaging the object under investigation. Due to the long observation times necessary and due to analytical problems (non-reproducible surface conditions, submicroscopic nature of the primary corrosion processes, etc.), neither is it generally possible to directly assess the protective action actually achieved by analyzing the progress of corrosion on the actual object to be protected. For this reason, numerous research projects have hitherto been carried out on the indirect determination of corrosive conditions with reference to relevant climatic data, for example humidity and temperature. However, it is common to all these investigations that only peripheral climatic conditions have been determined, but, due to the complex and as yet substantially unexplained corrosion mechanisms, it is not possible to come to any direct conclusions on the corrosive situation on the surface of the object of interest. In addition, very considerable equipment costs are necessary for this purpose, which are generally too expensive for practical use. Thus, each environmental factor whose effect on the corrosion process is to be taken into account must be determined individually, which means that, taking into account subclimatic differences, a large number of measurements and measurement sensors is necessary, even if only a single object is to be examined.